Znanstvenostručni
časopis Hrvatskog društva za geometriju i grafiku Scientific and Professional Journal 
 Ronaldo Garcia, Dimas Tejada (ragarcia@ufg.br, dimas.tejada@ues.edu.sv)
Principal Lines on an Ellipsoid in a Minkowski ThreeDimensional SpaceThe description of principal lines of the ellipsoid on the
3dimensional Minkowski space is established. A global
principal parametrization of a triple orthogonal system of
quadrics is also achieved, and the focal set of the ellipsoid
is sketched.

Boris Odehnal (boris.odehnal@uniak.ac.at)
A MiquelSteiner TransformationEach complete quadrilateral has three MiquelSteiner
points. Any triangle together with an arbitrarily chosen
point not on a triangle side also defines a complete quadrilateral, and thus, this pivot point defines three MiquelSteiner points. These three Miquel points form a triangle
which is perspective with the base triangle. The mapping
that assigns to the pivot point the uniquely defined perspector is a quadratic and not involutive Cremona transformation and shall be called MiquelSteiner transformation.
We shall study the action of the MiquelSteiner transformation and its inverse. 
 Walter Jank, Georg Glaeser, Boris Odehnal (georg.glaeser@uniak.ac.at, boris.odehnal@uniak.ac.at)
On the Geometry of Spherical TrochoidsWe provide a synthetic study of the topviews of spherical trochoids. These projections turn out to be higher trochoids, i.e., curves generated by the superposition of more than two rotations. Special shapes of these trochoids show up for special choices of the spherical radii of the rolling circles. A relation to closed algebraic curves of constant width is shown. These curves allow for a kinematic generation. Key words: spherical trochoid, rolling, evolute, involute,
curve of constant width 
Iva Kodrnja, Helena Koncul (iva.kodrnja@geof.unizg.hr,
helena.koncul@grad.unizg.hr)Locus Curves in Triangle FamiliesIn this article, we observe a oneparameter triangle family,
where two vertices are fixed and the third vertex lies on
a given line. For this family of triangles, we observe the
loci of centroids, orthocenters, circumcenters, incenters,
excenters and some triangle elements associated to these
triangle points. 
 Monika Đuzel, Ivana Filipan, Ljiljana Primorac Gajčić (monikadj@outlook.com, ivana.filipan@rgn.unizg.hr, lprimora@mathos.hr)
Curves in 3dimensional Minkowski SpaceIn this paper curves in threedimensional Minkowski space were analyzed and the main differences in local theory of curves in Euclidean and Minkowski space were emphasized. Special attention is paid to curves with no Euclidean counterpart. There are numerous examples of studied curves whose graphic representations were made by Mathematica software. Key words:
Minkowski space, spacelike curve, timelike
curve, lightlike curve 
 Vladimir Volenec, Ema Jurkin, Marija Šimić Horvath (volenec@math.hr, ema.jurkin@rgn.unizg.hr, marija.simic@arhitekt.hr)
Circles Related to a Complete QuadrangleThis paper presents an overview of some properties of a complete quadrangle ABCD in the Euclidean plane. We study the circles with diameters AB, AC, AD, BC, BD, and CD, as well as the pedal triangles and the pedal circles of the points A, B, C, D with respect to the triangles BCD, ACD, ABD and ABC, respectively. The presented results are known in literature, but here we prove them using a single method. Key words:
complete quadrangle, pedal triangles, pedal
circles 